Extension Springs

Extension Spring Manufacturing Specifications

SNM Hardware provides completely customized production of all springs and metal forms.

Large Volume Orders, Short Runs & Prototypes – formed, assembled and packaged to meet your requirements.
The probe inspection system for Superior Quality – ensures precision detection of dimensions, automatically isolating non-conforming products
Tech Centers –you can work with our team and equipment to optimize designs and lower costs.
Engineering Support – our team can provide expert design assistance on any order.

Shapes & Sizes

Spring End Types

Cross Center Hooks / Cross Loops
Draw Bars
Extended Machine Hooks
Expanded Hooks
Standard Machine Hooks
Rectangular Ends
Rectangular Ends with Swivel Hooks
Teardrop-Shaped Ends
Threaded Inserts
V-Hooks

Common Materials

Spring Steel
High/Low Carbon Steel
Nickel Plated Carbon Steel
Pre-plated Steel
Stainless Steel
Alloy
Non-Ferrous Metals
Elgiloy®、Hastelloy®、Monel®、Inconel®、Titanium
and More

Extension Spring Initial Tension

Most extension springs are wound with initial tension. This is an internal force that holds the extension spring’s coils together. The measure of the initial tension is the load necessary to overcome the internal force and begin coil separation. Unlike a compression spring that has zero load at zero deflection, an extension spring can have a preload at zero deflection (see graph). This built-in load, called initial tension, can be varied within limits, decreasing as the spring index increases.

Note that there is a range of stress (and, therefore, force) for any extension spring index that can be held without problems. If the designer needs an extension spring with no initial tension, the spring should be designed with space between the coils. Read more on initial tension.

Initial Tension (P1) is determined by extending the extension spring to a given length (L1) ensuring coil separation. The spring then is extended an equal distance to (L2). The amount of initial tension is equal to two (2) times the load achieved at (L1) minus the load at (L2). The formula for Initial Tension Simplified is (Pi) = 2P1 – P2.